In electrophotographic image forming apparatus, an image bearing member such as a drum-shaped photoreceptor is charged to form an electrostatic latent image, the electrostatic latent image is developed with toner to form a toner image on the image bearing member, the toner image is transferred onto a recording medium, and the toner image is then fixed to the recording medium. In this regard, foreign materials such as toner particles remain on the surface of the image bearing member after the toner image transferring process is performed. In order to prevent deterioration of image quality of the next toner image, a cleaner is provided to remove such foreign materials from the surface of the image bearing member. A cleaning blade, which is contacted with the surface of the image bearing member while moving relative to the image bearing member, has been typically used for the cleaner. JP-2011-197309-A discloses a cleaner which includes a cleaning blade in which plural layers including an edge layer are overlaid, wherein an edge of the edge layer is contacted with a surface of an image bearing member to clean the surface of the image bearing member. The cleaner has a property such that when the cleaner is used for a predetermined time while contacted with an image bearing member, the ratio (P160/P0) of the linear pressure (P160) of the edge layer to the image bearing member after 160 hours to the initial linear pressure (P0) is not lower than 90%, so that the cleaner can maintain the initial cleaning performance. In addition, physical properties of constitutional materials of the layers and thickness of the layers are specified therein.
FIG. 12A illustrates a conventional cleaning blade, and FIG. 12B is the cleaning blade cleaning a surface of an image bearing member. In an electrophotographic image forming apparatus, a photoreceptor 210 serving as an image bearing member moves (rotates) in a direction indicated by an arrow 220, and an electrostatic latent image is formed on the surface of the photoreceptor as the photoreceptor moves. After the electrostatic latent image is developed with toner to form a toner image on the photoreceptor, the toner image is transferred onto a recording medium such as a transfer paper. A cleaning blade 200 extends in a direction perpendicular to the moving direction 220 of the photoreceptor 210, and is arranged on a downstream side from a transferring device, which transfers the toner image from the photoreceptor to a recording medium, relative to the moving direction 220. The cleaning blade 200 rubs the surface of the photoreceptor 210 with the edge thereof to peel residual toner adhered to the surface of the photoreceptor, resulting in removal of the residual toner from the photoreceptor.
As illustrated in FIG. 12A, the cleaning blade 200 includes a right-angled edge 201, which is to be contacted with the surface of the photoreceptor 210, a first side surface 202, and a second side surface 203, wherein the edge 201 is present between the first and second side surfaces 202 and 203. When the cleaning blade 200 is in such a non-contact state as illustrated in FIG. 12A, the first side surface 202 is opposed to the surface of the photoreceptor 210. The cleaning blade 200 maintains this state when the cleaning blade is contacted with the surface of the photoreceptor 210.
FIG. 12B illustrates the cleaning blade 200 contacted with the surface of the photoreceptor 210. In this regard, the photoreceptor 210 moves in the direction 220, and when the edge 201 of the cleaning blade 200 is contacted with the surface of the photoreceptor 210, the edge is drawn by the photoreceptor toward the downstream side relative to the moving direction 220 (i.e., toward the first side surface 202) as illustrated in FIG. 12B. When the edge 201 is thus drawn by the photoreceptor 210, the edge portion is largely deformed and a wedge-shaped portion 204 is formed. The wedge-shaped portion 204, which is contacted with the surface of the photoreceptor 210, rubs the surface of the photoreceptor as the photoreceptor moves. In this case, the first side surface 202 is not contacted with the surface of the photoreceptor 210.
When the cleaning blade 200 is thus contacted with the photoreceptor 210, the contact area is relatively wide, and therefore the contact pressure is relatively low. Therefore, residual toner on the surface of the photoreceptor 210 tends to pass through the nip between the wedge-shaped portion 204 of the cleaning blade 200 and the surface of the photoreceptor, resulting in deterioration of the cleaning ability of the cleaning blade.
In this regard, when the hardness of the cleaning blade 200 is increased in order to prevent large deformation of the edge 201 and to decrease the area of contact of the cleaning blade with the surface of the photoreceptor 210, the cleaning blade tends to cause plastic deformation after long repeated use.
Recently, countermeasures such that a protective agent including an inorganic lubricant is applied on the surface of a photoreceptor, or toner including a lubricant including a fatty acid metal salt such as zinc stearate is used to enhance the abrasion resistance of the photoreceptor have been taken to enhance the cleaning property of the photoreceptor. However, even when such countermeasures are taken, it is hard to enhance the cleaning property of the photoreceptor if such a conventional cleaning blade as mentioned above, which forms a wedge-shaped portion at the edge thereof, is used.
FIGS. 13A and 13B illustrate the photoreceptor 210 on which a protective agent including an inorganic lubricant is applied to enhance the cleaning property of the photoreceptor, and the conventional cleaning blade 200 contacted with the surface of the photoreceptor. In FIGS. 13A and 13B, numerals 300 and 301 respectively denote residual toner and a protective agent.
As illustrated in FIG. 13A, when the edge 201 of the cleaning blade 200 is contacted with the surface of the photoreceptor 210, the edge 210 is largely deformed so as to have the wedge-shaped portion 204. Since the wedge-shaped portion 204 is contacted with the photoreceptor 210, the contact pressure of the cleaning blade 200 is relatively low, resulting in deterioration of the cleaning ability of the cleaning blade. Therefore, the protective agent 310 passes through the nip between the cleaning blade 200 and the surface of the photoreceptor 210 and remains on the surface of the photoreceptor 210.
FIG. 13B illustrates the state of the cleaning blade and the photoreceptor after the image forming operation is continued. Since the protective agent 310 continues to pass through the nip between the cleaning blade 200 and the surface of the photoreceptor 210, the protective agent 310 grows and enlarges on the surface of the photoreceptor, and therefore the residual toner 300 easily passes through the nip, thereby forming abnormal images such as white omissions and vertical streak images.
FIG. 14 illustrates an image forming apparatus in which a toner 340 including a lubricant including zinc stearate is used for improving the abrasion resistance of the photoreceptor 210 and which uses an intermediate transfer belt 250 moving in a direction indicated by an arrow 260 while being contacted with the surface of the photoreceptor. A toner image formed on the surface of the photoreceptor 210 by developing an electrostatic latent image thereon is transferred to the intermediate transfer belt 250. The toner image on the intermediate transfer belt 250 is then transferred onto a recording medium (not shown in FIG. 14). Numeral 270 denotes a developing roller to supply the toner 340 to the photoreceptor 210.
Such a toner 340 including a lubricant such as zinc stearate has a relatively low charge quantity (i.e., low charging ability), and when the toner is charged by the transfer current, the toner has a reverse charge (a positive (+) charge in FIG. 14), and the reversely charged toner is transferred to the intermediate transfer belt 250. Since the toner 340 has a relatively low charge quantity, the amount of the reversely charged toner and the charge quantity thereof are increased in the transferring process in which the toner image is transferred to the intermediate transfer belt 250. Therefore, the amount of residual toner, which remains on the surface of the photoreceptor 210 without being transferred, increases. Therefore, a relatively large amount of residual toner reaches the cleaning blade 200, i.e., the cleaning blade has to remove a relatively large amount of residual toner from the surface of the photoreceptor 210.
The cleaning blade 200 illustrated in FIG. 14 also causes such deformation as illustrated in FIG. 12 at the edge thereof, and the wedge-shaped portion 204 is formed. Since the wedge portion 204 is contacted with the surface of the photoreceptor 210, the contact pressure of the cleaning blade 200 is relatively low, resulting in deterioration of the cleaning ability of the cleaning blade. Therefore, the amount of toner passing through the nip between the cleaning blade 200 and the surface of the photoreceptor 210 increases, resulting in defective cleaning, thereby deteriorating the toner image quality.
FIG. 15 illustrates an image forming apparatus in which a toner 340 including a lubricant including zinc stearate is used to enhance the abrasion resistance of the photoreceptor 210 and the photoreceptor includes a particulate inorganic material 360 in a surface portion thereof to enhance the abrasion resistance thereof.
The photoreceptor 210 including the particulate inorganic material 360 has a rough surface 370. In addition, since the toner 340 including a lubricant such as zinc stearate has a relatively low charge quantity (i.e., low charging ability), the amount of toner, which is reversely charged by the transfer charger, increases. Therefore, the adhesion force of residual toner 340, which remains on the photoreceptor 210 without being transferred, increases.
The cleaning blade 200 illustrated in FIG. 15 also causes such deformation as illustrated in FIG. 12 at the edge thereof, and the wedge-shaped portion 204 is formed. Since the wedge portion 204 is contacted with the surface of the photoreceptor 210, the contact pressure of the cleaning blade 200 is relatively low. In addition, since the rough surface 370 is formed on the photoreceptor 210, the cleaning blade 200 is unevenly and unstably contacted with the surface of the photoreceptor 210, and therefore the amount of toner passing through the nip between the cleaning blade and the surface of the photoreceptor increases, resulting in defective cleaning, thereby deteriorating the toner image quality.